A glyph, U with umlaut, appears in the German alphabet. It represents the umlauted form of u, which results in the same sound as the [y]. It can also represent [ʏ]. The letter is collated together with U, or as UE. In languages that have adopted German names or spellings, such as Swedish, the letter also occurs. It is however not a part of these languages' alphabets. In Swedish the letter is called tyskt y which means German y.

In other languages that do not have the letter as part of the regular alphabet or in limited character sets such as ASCII, U-umlaut is frequently replaced with the two-letter combination "ue". Software for optical character recognition sometimes sees it falsely as ii.

This same letter appears in the ChineseRomanisationspinyin, Wade-Giles, and the German-based Lessing-Othmer, where it represents the same sound [y]: 綠/lü (green) or 女/nü (female). Standard Mandarin Chinese pronunciation has both the sounds [y] and [u]. Pinyin only uses "Ü" to represent [y] after the letters "L" or "N" to avoid confusion with words such as 路/lu (road) and 怒/nu (anger). Words such as 玉/yu (jade) or 句/ju (sentence) are pronounced with [y], but are not spelled with "Ü". Although Wade-Giles and Lessing use Ü in all situations. As the letter "Ü" is missing on most keyboards and the letter "V" is not present in standard Mandarin pinyin, the letter "V" is used on most computer Chinese input methods to enter the letter "Ü". As a result, romanisation of Chinese with the letter "V" representing the Ü sound is sometimes found.

Several languages use diaeresis over the letter U to show that the letter is pronounced in its regular way, without dropping out, building diphthongs with neighbours, etc.

In Spanish, it is used to distinguish between "gue"/"güe" [ɡe]/[ɡwe] and "gui"/"güi" [ɡi]/[ɡwi]: nicaragüense (Nicaraguan), pingüino (penguin).

Similarly in Catalan, "gue~güe" are [ɡe]~[ɡwe], "gui~güi" are [ɡi]~[ɡwi], "que~qüe" are [ke]~[kwe] and "qui~qüi" are [ki]~[kwi],
as in aigües, pingüins, qüestió, adeqüi. Also, ü is used to mark that vowel pairs that normally would form a diphthong must be pronounced as separate syllables, examples: Raül, diürn.

In French, the diaeresis appears over the "u" only very rarely, in some uncommon words, capharnaüm[-aɔm] ('shambles'), Capharnaüm/Capernaüm[-aɔm] or Emmaüs[-ays]. After the 1990 spelling reforms, it is applied to a few more words, like aigüe (formerly aiguë), ambigüe (formerly ambiguë) and argüer[aʁɡɥe] (formerly without the diaeresis).

Historically the unique letter Ü and U-diaeresis were written as a U with two dots above the letter. U-umlaut was written as a U with a small e written above: this minute e degenerated to two vertical bars in medievalhandwritings. In most later handwritings these bars in turn nearly became dots.

In modern typography there was insufficient space on typewriters and later computer keyboards to allow for both a U-with-dots (also representing Ü) and a U-with-bars. Since they looked near-identical the two glyphs were combined, which was also done in computer character encodings such as ISO 8859-1. As a result, there was no way to differentiate between the three different characters. While Unicode theoretically provides a solution,[how?] this is almost never used.

Using the Swiss French keyboard, ⟨ü⟩ can be entered by typing ⇧ Shift+È

Using the US International layout, ⟨ü⟩ can be entered by typing AltGR+Y

Microsoft Windows: with the Number Lock on, hold down the Alt key while typing on the numeric keypad the decimal value of the code point from the active DOS/OEM code page without a leading zero, then release the Alt key; i.e. Alt+1+5+4 for ⟨Ü⟩ and Alt+1+2+9 for ⟨ü⟩

Microsoft Windows: with the Number Lock on, hold down the Alt key while typing on the numeric keypad the decimal value of the code point from the active ANSI code page with a leading zero, then release the Alt key; i.e. Alt+0+2+2+0 for ⟨Ü⟩ and Alt+0+2+5+2 for ⟨ü⟩

Microsoft Word for Windows: type Ctrl+: followed by ⇧ Shift+U for ⟨Ü⟩ or Ctrl+: then U for ⟨ü⟩

macOS with an English keyboard layout (Australian, British, or US): type ⌥ Option+U followed by ⇧ Shift+U for ⟨Ü⟩ or ⌥ Option+U and then U for ⟨ü⟩ or by keeping the U key pressed and then typing 2

In GTK-based GUI-Applications, Ctrl+⇧ Shift+ufollowed by the Hex-Code and ↵ Enter

On systems with a Compose key, Compose, followed by " and U for ⟨Ü⟩, and Compose, ", u for ⟨ü⟩